Core-Shell InGaN/AlGaN Quantum Nanowire Photonic Structures

ABSTRACT

A nanowire can include a first semiconductor portion, a second portion including a quantum structure disposed on the first portion, and a second semiconductor portion disposed on the second portion opposite the first portion. The quantum structure can include one or more quantum core structures and a quantum core shell disposed about the one or more quantum core structures. The one or more quantum core structures can include one or more quantum disks, quantum arch-shaped forms, quantum wells, quantum dots within quantum wells or combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a divisional application of U.S. patent applicationSer. No. 16/044,337 filed Jul. 24, 2018, which claims the benefit ofU.S. Provisional Patent Application No. 62/536,449 filed Jul. 24, 2017,both of which are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

Computing systems have made significant contributions toward theadvancement of modem society and are utilized in a number ofapplications to achieve advantageous results. Numerous devices, such asdesktop personal computers (PCs), laptop PCs, tablet PCs, netbooks,smart phones, servers, and the like have facilitated increasedproductivity and reduced costs in communicating and analyzing data inmost areas of entertainment, education, business, and science. Onecommon aspect of computing devices and other electronics are displaysbased on Light-Emitting Diodes (LEDs).

Scalable and efficient light emitting photonic devices are needed for abroad range of applications including lighting, display, communication,sensing, imaging and medical diagnostics. While Gallium Nitride (GaN)based Light Emitting Diodes (LEDs) exhibit efficient operation in theblue wavelength range, their efficiency and stability degradeconsiderably with increasing wavelength, leading to a “green gap” in LEDand laser technologies. The quantum efficiency parameter η of asemiconductor light emitter can be determined by Equation 1:

$\begin{matrix}{\eta \propto \frac{\tau_{r}^{- 1}}{\tau_{r}^{- 1} + \tau_{nr}^{- 1}}} & (1)\end{matrix}$

wherein the two parameters τ_(r) and τ_(nr) represent the radiative andnonradiative lifetime in the device action region respectively. Inconventional Indium Gallium Nitride/Gallium Nitride (InGaN/GaN) greenand amber LEDs, the presence of large densities of defects anddislocations, due to the large lattice mismatch of approximately 11%between InN and GaN, and Auger recombination leads to a small τ_(nr) andtherefore low quantum efficiency. Moreover, the performance ofconventional InGaN light emitters suffers from strain-inducedpolarization fields and the resulting quantum-confined Stark effect,which often results in a considerable blueshift in emission wavelengths(up to 30 nm) under high power operation. To date, a clear path toachieve efficient and stable semiconductor light emitters operating inthe green, yellow, and amber wavelengths has remained elusive.

Emission properties of a semiconductor light emitter can be determinednot only by the properties of the device active medium but also by theoptical density of states surrounding the active region. For example, byexploiting the Purcell effect in an optical microcavity, the radiativelifetime τ_(r) can be significantly reduced, thereby leading to anenhancement of the internal quantum efficiency which is denoted by theparameter η. To date, however, there has been few demonstrations on theuse of Purcell effect to bridge the “green gap” in semiconductor LEDsand lasers. The Purcell factor, Fp, is determined by Equation 2:

$\begin{matrix}{F_{p} \propto \frac{Q_{g}}{V}} & (2)\end{matrix}$

wherein Q is the quality factor, V is the mode volume of the opticalcavity, and g is the mode degeneracy. To enhance the Purcell factor,conventional design considerations are focused on small optical cavitysize (on the order of micron meter), whereas practical LED devicesrequire extended optical mode spread over millimeter scale (i.e. threeto six orders of magnitude larger than conventional designs). Inaddition, previously reported GaN optical cavities, including photoniccrystals, are generally fabricated from crystalline epilayers using thetop-down etching method, which inherently have large densities ofdefects and dislocations, with emission wavelengths limited to the blueand near-ultraviolet spectral range. Accordingly, there is a continuingneed for improved optoelectronic devices.

SUMMARY OF THE INVENTION

The present technology may best be understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the present technology directed towardcore/shell quantum nanowire photonic structures.

In one embodiment, a nanowire can include a first group III-V compoundsemiconductor with a first type of doping. One or more quantum corestructures and a quantum shell structure disposed about the one or morequantum core structures can be disposed on the first group III-Vcompound semiconductor with the first type of doping. A second groupIII-V compound semiconductor with a second type of doping can bedisposed on the portion including the one or more quantum corestructures with quantum shell structure disposed about the quantum corestructures.

In another embodiment, a device can include one or more clusters ofnanowires. The nanowires can include a first semiconductor region, acore-shell quantum structure, and a second semiconductor region. Thecore-shell quantum structure can include one or more quantum corestructures and a quantum shell structure disposed about the one or morequantum core structures. The one or more quantum core structures caninclude one or more alternating layers of Indium Gallium Nitride (InGaN)layers and one or more layers of Aluminum Gallium Nitride (AlGaN). Thequantum shell structure can include AlGaN or Aluminum-rich GalliumNitride (GaN). The first semiconductor region can include n-type dopedGallium Nitride (GaN), and the second semiconductor region can includep-type doped Gallium Nitride (GaN).

In another embodiment, a method of fabricating a nanowire can includeforming by Selective Area Growth (SAG) a first semiconductor nanowireregion with a first type of doping. A quantum structure can be formed bySAG on the first semiconductor nanowire region. The quantum structurecan include one or more quantum core structures and a quantum shellstructure disposed about a periphery of the one or more quantum corestructures. A second semiconductor nanowire region with a second type ofdoping can be formed by SAG on the quantum structure.

In yet another embodiment, a method of fabricating a device includingone or more clusters of nanowires can include forming a nano-patternlayer including one or more cluster of openings on a substrate. A firstsemiconductor region with a first type of doping can be formed in theone or more cluster of openings in the nano-pattern layer. The firstsemiconductor region can be formed by epitaxially depositing n-typedoped Gallium Nitride (GaN). A quantum structure can be formed on thefirst semiconductor region. The quantum structure can include one ormore quantum core structures and a quantum shell structure disposedabout a the one or more quantum core structures. The one or more quantumcore structures can be formed by alternatively epitaxially depositingone or more layers of Indium Gallium Nitride (InGaN) and one or morelayer of Aluminum Gallium Nitride (AlGaN). The epitaxial deposition ofAluminum Gallium Nitride (AlGaN) on the Indium Gallium Nitride (InGaN)also results in the formation of the quantum shell structure thatincludes Aluminum Gallium Nitride (AlGaN) or Aluminum-rich GalliumNitride (GaN). A second semiconductor region with a second type ofdoping can be formed on the quantum structure. The second semiconductorregion can be formed by epitaxially depositing p-type doped GalliumNitride (GaN).

In accordance with aspects of the present technology, devices formed ofInGaN can be synthesized via a bottom-up method, wherein the formationof defects and dislocations are minimized due to the efficient surfacestrain relaxation. With the use of selective area epitaxy, the size,spacing and morphology of InGaN nanowire structures (includingdot-in-nanowires, nanotriangles and nano-rectangles, for example) can beprecisely controlled, and, as such, spatially extended band edge modescan develop over a large area of such defect-free photonic crystals. Thepresent techniques can form InGaN-based light emitters where there is anabsence of Varshni and quantum-confined Stark, factors that contributesignificantly to the efficiency drop and device instability under highpower operation that plagues convention light emitters. The resultingdevices have distinct emission properties that stem directly from thehighly-stable and scalable band edge modes of the InGaN photoniccrystalline structures, in particular due to the precisely controlledsize, position, and morphology of InGaN photonic molecules. Theresulting devices can be applied for varied LED and laser operations,including, in particular, uncooled, high efficiency operation.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present technology are illustrated by way of exampleand not by way of limitation, in the figures of the accompanyingdrawings and in which like reference numerals refer to similar elementsand in which:

FIG. 1 shows a nanowire, in accordance with aspects of the presenttechnology.

FIG. 2 shows a method of fabricating a nanowire, in accordance withaspects of the present technology.

FIG. 3 shows a nanowire device, in accordance with aspects of thepresent technology.

FIGS. 4A and 4B show a method of fabricating a nanowire device, inaccordance with aspects of the present technology.

FIG. 5 shows an exemplary nano-pattern, in accordance with aspects ofthe present technology.

FIGS. 6A-6D show exemplary nano-patterns, in accordance with aspects ofthe present technology.

FIG. 7 shows and exemplary Scanning Electron Microscope (SEM) images ofhexagonal nanowire structures, in accordance with aspects of the presenttechnology.

FIG. 8 shows and exemplary SEM images of hexagonal nanowire structures,in accordance with aspects of the present technology.

FIG. 9 shows and exemplary SEM images of hexagonal nanowire structures,in accordance with aspects of the present technology.

FIG. 10 shows a plot of an exemplary photoluminescence emissionspectrum, in accordance with aspects of the present technology.

FIG. 11 shows an exemplary plot of light intensity versus excitationpower, in accordance with aspects of the present technology.

FIG. 12 shows a diagram of simulated photonic crystals, in accordancewith aspects of the present technology.

FIG. 13 shows an exemplary electric field profile, in accordance withaspects of the present technology.

FIGS. 14A-14C show exemplary cathodoluminescences for crystals ofdifferent areal sizes, in accordance with aspects of the presenttechnology.

FIG. 15 the spectrally resolved cathodoluminescence mapping imagescollected at various wavelengths.

FIG. 16 shows a cathodoluminescence mapping image, in accordance withaspects of the present technology.

FIG. 17 shows exemplary plots associate with the variations of theluminescence intensity and spectral linewidth, in accordance withaspects of the present technology.

FIG. 18 shows plots of photoluminescence emission spectra for variousnanowire structure heights, in accordance with aspects of the presenttechnology.

FIG. 19 shows normalized photoluminescence emission spectra, inaccordance with aspects of the present technology.

FIG. 20 shows exemplary plots of the peak emission wavelength andspectral linewidth versus pumping power, in accordance with aspects ofthe present technology.

FIG. 21 shows exemplary plots of luminescence emission spectra of InGaNnanowire structures, in accordance with aspects of the presenttechnology.

FIG. 22 shows exemplary plots associated with the variations of theemission wavelength peak with temperature and the variations of spectrallinewidth with temperature, in accordance with aspects of the presenttechnology.

FIG. 23 shows an array of nanowire structures and an associatedphotoluminescence emission pattern, in accordance with aspects of thepresent technology.

FIG. 24 shows the emission stability of InGaN nanowire structures acrossa large area, accordance with aspects of the present technology.

FIG. 25 shows the emission stability of InGaN nanowire structures acrossa large area, accordance with aspects of the present technology.

FIG. 26 shows the photoluminescence emission spectra of the InGaNnanowires, accordance with aspects of the present technology.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the presenttechnology, examples of which are illustrated in the accompanyingdrawings. While the present technology will be described in conjunctionwith these embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the scope of the invention asdefined by the appended claims. Furthermore, in the following detaileddescription of the present technology, numerous specific details are setforth in order to provide a thorough understanding of the presenttechnology. However, it is understood that the present technology may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail as not to unnecessarily obscure aspects of the presenttechnology.

Some embodiments of the present technology which follow are presented interms of routines, modules, logic blocks, and other symbolicrepresentations of operations on data within one or more electronicdevices. The descriptions and representations are the means used bythose skilled in the art to most effectively convey the substance oftheir work to others skilled in the art. A routine, module, logic blockand/or the like, is herein, and generally, conceived to be aself-consistent sequence of processes or instructions leading to adesired result. The processes are those including physical manipulationsof physical quantities. Usually, though not necessarily, these physicalmanipulations take the form of electric or magnetic signals capable ofbeing stored, transferred, compared and otherwise manipulated in anelectronic device. For reasons of convenience, and with reference tocommon usage, these signals are referred to as data, bits, values,elements, symbols, characters, terms, numbers, strings, and/or the likewith reference to embodiments of the present technology.

It should be borne in mind, however, that all of these terms are to beinterpreted as referencing physical manipulations and quantities and aremerely convenient labels and are to be interpreted further in view ofterms commonly used in the art. Unless specifically stated otherwise asapparent from the following discussion, it is understood that throughdiscussions of the present technology, discussions utilizing the termssuch as “receiving,” and/or the like, refer to the actions and processesof an electronic device such as an electronic computing device thatmanipulates and transforms data. The data is represented as physical(e.g., electronic) quantities within the electronic device's logiccircuits, registers, memories and/or the like, and is transformed intoother data similarly represented as physical quantities within theelectronic device.

In this application, the use of the disjunctive is intended to includethe conjunctive. The use of definite or indefinite articles is notintended to indicate cardinality. In particular, a reference to “the”object or “a” object is intended to denote also one of a possibleplurality of such objects. It is also to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

FIG. 1 shows a nanowire, in accordance with aspects of the presenttechnology. The nanowire 100 can include a first semiconductor region110, a core-shell quantum structure 120-140 disposed on the firstsemiconductor region 110, and a second semiconductor region 150 disposedon the core-shell quantum structure 120-140 opposite the firstsemiconductor region 110. In one implementation, the first semiconductorregion 110 can include a group III-V compound semiconductor with a firsttype of doping, such as n-dope Gallium Nitride (GaN). The secondsemiconductor region 150 can include a group III-V compoundsemiconductor with a second type of doping, such as p-doped GaN. Inaspects, the nanowire 100 can have a substantially hexagonal, square,rectangular, rhombic, polygonal, circular or elliptical cross-sectionalshape.

In aspects, the core-shell quantum structure 120-140 can include one ormore quantum core structures 120, 130, and a quantum shell structure 140disposed about a periphery of the one or more quantum core structures120, 130. The one or more quantum core structures 120, 130 can includeone or more quantum disks, quantum arch-shaped forms, quantum wells,quantum dots within quantum wells or combinations thereof. Thecore-shell quantum structure can include one or more alternating quantumactive regions 120 and quantum barrier regions 130. In oneimplementation, the one or more quantum core structures 120, 130 caninclude one or more alternating layers of Indium Gallium Nitride (InGaN)and Aluminum Gallium Nitride (AlGaN) 130. For example, a first layer ofInGaN 120 can be disposed on the n-doped GaN of the first semiconductorregion 110, and a first layer of AlGaN 130 disposed on the first layerof InGaN 120. A second layer of InGaN can be disposed on the first layerof AlGaN 130, and a second layer of AlGaN can be disposed on the secondlayer of InGaN. The layers of InGaN and AlGaN can be alternatelyrepeated to form a predetermined number of quantum core structures. Inan exemplary implementation, the nanowire 110 can include ten quantumcore structures formed by ten layers of InGaN interleaved with tenlayers of AlGaN. In one implementation, the quantum shell structure 140can include AlGaN or Aluminum-rich Gallium Nitride disposed about thealternating layers of InGaN and AlGaN of the one or more quantum corestructures 120, 130. An AlGaN compound semiconductor can be used toachieve a nanowire having ultraviolet wavelengths of emission. Inanother implementation, the one or more quantum barrier regions 130 caninclude Indium Gallium Arsenide (InGaAs) to achieve a nanowire havinginfrared wavelengths of emission. In yet another implementation, the oneor more quantum barrier regions 130 can include Indium Arsenide (InAs)to achieve a nanowire having mid-infrared wavelengths of emission.

Referring now to FIG. 2 a method of fabricating a nanowire, inaccordance with aspects of the present technology, is shown. The methodof fabricating the nanowire can include forming a first portion of thenanowire 110 (also referred to as a lower portion) including a groupIII-V compound semiconductor with a first type of doping on a substrate,at 210. In one implementation, the group III-V compound semiconductorwith the first type of doping can be n-dope Gallium Nitride (GaN). Thesubstrate can be a Silicon Carbide (SiC) substrate, a Gallium Nitride(GaN) substrate, a Silicon Oxide (SiOx) substrate, a Sapphire substrate,an Aluminum Oxide (AlOx) substrate, a quartz substrate, a metalsubstrate, or a combination thereof. In one implementation, the groupIII-V compound semiconductor with the first type of doping can be formedby selective area epitaxy of the group III-V compound semiconductor withthe first type of doping on the substrate. For example, the lowerportion of the nanowire 110 can be formed by selective area epitaxy ofGaN with Silicone (Si) doping (e.g., n-doping) on top of anano-patterned substrate using plasma assisted Molecular Beam Epitaxy(MBE) to form the lower portion of the nanowire 110 with across-sectional width (also referred to a lateral size) of approximately200 nm and a height of approximately 380 to 460 nanometers (nm). Thegrowth conditions for the Si-doped GaN can include a grow temperature ofapproximately 800 degrees Centigrade (° C.), with a nitrogen flow rateof approximately 0.6 standard cubic centimeter per minute (sccm), aforward plasma power of approximately 350 Watts (W), and a Ga BeamEquivalent Pressure (BEP) of approximately 3.5×10⁻⁷ Torr.

The method of fabrication can include forming a core-shell quantumstructure including one or more core quantum structures and a shellquantum structure. At 220, a first quantum active region 120 can beformed. In one implementation, Indium Gallium Nitride (InGaN) can beformed by selective area epitaxy on the Silicone doped GaN to form thefirst quantum active region 120 with a height of approximately 5 nm. TheInGaN can be deposited using plasma assisted MBE, wherein the growthconditions can include a substrate temperature of approximately 600° C.,a Ga BEP of approximately 9×10⁻⁹ Torr and In BEP of approximately7.5×10⁻⁸.

At 230, a first quantum barrier region 130 can be deposited. In oneimplementation, Aluminum Gallium Nitride (AlGaN) can be formed byselective area epitaxy on the InGaN for form the first quantum barrierregion 130 with a height of approximately 5 nm. For example, the AlGaNcan be deposited using plasma assisted MBE, wherein the growthconditions can include a substrate temperature of approximately 600° C.,a Ga BEP of approximately 9×10⁻⁹ Torr, and Al BEP of approximately4.5×10⁻⁹. The incorporation of AlGaN in the quantum barrier region 130leads to the formation of an AlGaN or Aluminum-rich GaN shellsurrounding the one or more InGaN quantum active regions due to thesmaller Al adatom migration length compared to Ga and In adatoms.

An AlGaN compound semiconductor can be used for the quantum barrierregion 130 to achieve a nanowire having ultraviolet wavelengths ofemission. In another implementation, the quantum barrier region 130 caninclude Indium Gallium Arsenide (InGaAs) to achieve a nanowire havinginfrared wavelengths of emission. In yet another implementation, thequantum barrier region 130 can include Indium Arsenide (InAs) to achievea nanowire having mid-infrared wavelengths of emission.

The processes at 220 and 230 can be performed one or more times to formthe second portion of the nanowire. For example, the processes at 220and 230 can be iteratively performed ten times to form a second portionof the nanowire including ten quantum core structures and a quantumshell structure disposed about the periphery of the ten quantum corestructures.

At 240, a second portion of the nanowire 150 (also referred to as anupper portion) including a group III-V compound semiconductor with asecond type of doping can be formed. In one implementation, the groupIII-V compound semiconductor with the first type of doping can be p-dopeGallium Nitride (GaN). The group III-V compound semiconductor with thesecond type of doping can be deposited by selective area epitaxy. Forexample, supper portion of the nanowire 150 can be formed by selectivearea epitaxy of GaN with Magnesium (Mg) doping (e.g., p-doping) on topof a quantum barrier region and surrounding quantum shell structure 140using plasma assisted Molecular Beam Epitaxy (MBE) to form the upperportion of the nanowire 150 with height of approximately 30 to 80 nm.The growth conditions for the Mg-doped GaN can include a Ga BEP ofapproximately 3.5×10⁻⁷ Torr, a Mg BEP of approximately 2×10⁻⁹ and asubstrate temperature of approximately 750° C.

The incorporation of AlGaN in the one or more quantum barrier regions130 of the core-shell quantum structure 120-140, instead of GaN barriersas used in the conventional art, advantageously leads to the formationof the AlGaN quantum shell structure 140 surrounding the quantum corestructure 120, 130. This particular core-shell quantum structure 120-140formation process is due to the smaller Al adatom migration lengthcompared to Ga and In adatoms. The resulting core-shell quantumstructure 120-140 can advantageously suppress non-radiative surfacerecombination resulting an enhanced luminescence intensity andluminescence efficiency of the nanowire 100.

Referring now to FIG. 3 , a nanowire device, in accordance with aspectsof the present technology, is shown. The nanowire device 300 can includeone or more clusters of nanowires 310 disposed on a nano-patternedsubstrate 315-325. The nanowires 310 can have a structure as describedabove with regard to FIGS. 1 .

In one implementation, the nano-patterned substrate 315-325 can includea nano-pattern layer 315 including one or more clusters of openingsdisposed on a substrate 320. Optionally, a nucleation layer 325 can bedisposed between the nano-pattern layer 315 and the substrate 320. Inone implementation, the nano-pattern layer 315 can include Titanium(Ti), Silicon Nitride (SiNx), Silicon Oxide (SiOx), or the like. Thesubstrate 320 can be a Silicon (Si) substrate, a Silicon Carbide (SiC)substrate, a Gallium Nitride (GaN) substrate, a Silicon Oxide (SiOx)substrate, a Sapphire substrate, an Aluminum Oxide (AlOx) substrate, anAluminum Nitride (AlN) substrate, a quartz substrate, a metal substrate,or a combination thereof. The optional nucleation layer 325 can includeGallium Nitride (GaN), Aluminum Nitride (AlN), SiNx, Gallium Arsenide(GaAs) or the like. The one or more clusters of nanowires 310 can bedisposed on the substrate 320 through the one or more clusters ofopenings in the nano-pattern layer 315. The nucleation layer 325 can beconfigured to promote a crystalline structure in the group III-Vcompound semiconductor with a first type of doping of the lower portionof the nanowire 110.

The nanowire device 300 can also include one or more first contacts330-340 that can be disposed on the one or more cluster of nanowires 310opposite the substrate 315-325. In one implementation, a plurality offirst contacts 330-340 can be configured to couple to different clustersof nanowires 300. For example, FIG. 3 illustrates a single first contact330-340 configured to be coupled to a cluster of twelve nanowires 310.The device can include one or more sets of clusters of nanowires 310with corresponding separate first contacts 330-340. In oneimplementation, the one or more first contacts 330-340 can include afirst layer 330 of Nickle (Ni), Gold (Au) and/or NiAu alloys thereof, asecond layer 335 of Indium Tin Oxide (ITO) disposed on the first layer330 and coupled to the plurality of nanowires 310, and a third layer 340of Nickle (Ni), Gold (Au) and/or NiAu alloys thereof disposed on thesecond layer 334. The second layer 335 of ITO can be configured topermit light to pass through. The first and third layers 330, 340 can beconfigured to make good ohmic contact with the nanowires 310 through thesecond layer 335, and can include one or more windows to permit light topass through. The nanowires device 300 can further include an opticallytransmissive layer 345 disposed about the one or more clusters ofnanowires 310 between the substrate 315-325 and the one or more firstcontacts 330-340. In one implementation, the optically transmissivelayer 345 can be a polyimide. One or more second contacts 350 can bedisposed on the substrate 315-325 opposite the one or more clusters ofnanowires 310. The one or more second contacts 350 can be electricallycoupled to the nanowires 310 through the substrate 315-325. In oneimplementation, the one or more second contacts 350 can include one ormore layers of Titanium (Ti), Gold (Au) and/or TiAu alloys thereof. Thesubstrate 320 can be a heavily n-doped silicon (Si) substrate to make agood ohmic contact between the second contact 350 and the one or moreclusters of nanowires 310.

Referring now to FIGS. 4A and 4B, a method of fabricating a nanowiredevice, in accordance with aspects of the present technology, is shown.The method of fabrication can include optionally forming a nucleationlayer on a substrate, at 410. In one implementation, the substrate canbe a Silicon (Si) substrate, a Silicon Carbide (SiC) substrate, aGallium Nitride (GaN) substrate, a Silicon Oxide (SiOx) substrate, aSapphire substrate, an Aluminum Oxide (AlOx) substrate, an AluminumNitride (AlN) substrate, a quartz substrate, a metal substrate, or acombination thereof. The optional nucleation layer 325 can includeGallium Nitride (GaN), Aluminum Nitride (AlN), SiNx, Gallium Arsenide(GaAs) or the like. In one implementation a layer of GaN approximately 4micrometers (μm) can be deposited on an Al₂O₃ (0001) substrate by ande-beam evaporative deposition process.

At 420, a nano-pattern layer including one or more clusters of openingscan be formed on the substrate or if applicable the optional nucleationlayer. The nano-pattern layer can be characterized by a predeterminedspacing. In one implementation, a layer of Titanium (Ti), or othermaterials such as Silicon Nitride (SiNx) or Silicon Oxide (SiOx), can bedeposited. A polymethyl methacrylate (PMMA) layer can be deposited andpattern by an e-beam lithography process to include one or more clustersof openings. The portions of the Ti layer exposed by the patterned PMMAlayer can be etched using a reactive dry etching technique to form a Tilayer including one or more cluster of openings. The patterned Ti layercan be subject to a surface nitridation for approximately 10 minutes at400° C. The exposed portions of the substrate or optional nucleationlayer exposed by the patterned Ti layer can be cleaned by HydrogenChloride (HCl).

Referring now to FIG. 5 , an exemplary nano-pattern, in accordance withaspects of the present technology, is shown. In the exemplarynano-pattern, a cluster of seven hexagonal openings/nanowirescharacterized by a predetermined spacing is illustrated. The clusters ofopenings/nanowires can be characterized by a cross-sectional width d(also referred to as lateral size) 510, separation a (also referred toas lattice constant) 520, and the reciprocal lattice vectors M 530 and K540 both emanating from a center point F 560. The cross-sectional widthd 510 and separation a 520 are not the same size. In one implementation,the cross-sectional width d 510 relative to the separation a 520 can beindicated by the relationship d=0.85a.

Referring again to FIG. 4 , a lower portion of the nanowires 110 in theone or more clusters can be formed in the one or more clusters ofopening in the nano-pattern layer, at 430. The lower portion of thenanowire can include a group III-V compound semiconductor with a firsttype of doping formed on the substrate through the one or more clusterof openings in the nano-pattern layer. The cross-sectional width d 510and separation a 520 are not the same size. In one implementation, thecross-sectional width d 510 relative to the separation a 520 can beindicated by the relationship d=0.85a. In one implementation, the lowerportion of the nanowire 110 can be formed by selective area epitaxy ofGaN with Silicone (Si) doping (e.g., n-doping) on top of the substratethrough the one or more cluster of openings in the nano-patterned layerusing plasma assisted Molecular Beam Epitaxy (MBE) to form the lowerportion of the nanowire 110 with a cross-sectional width (also referredto as lateral size) of approximately 200 nm and a height ofapproximately 380 to 460 nanometers (nm). The growth conditions for theSi-doped GaN can include a grow temperature of approximately 800 degreesCentigrade (° C.), with a nitrogen flow rate of approximately 0.6standard cubic centimeter per minute (sccm), a forward plasma power ofapproximately 350 Watts (W), and a Ga Beam Equivalent Pressure (BEP) ofapproximately 3.5×10⁻⁷ Torr. The one or more clusters of nanowires canbe characterized by a cross-sectional width d (also referred to aslateral size) 510, separation a (also referred to as lattice constant)520, and the reciprocal lattice vectors M 530 and K 540 both emanatingfrom a center point I 560, as illustrated in FIG. 5 .

The method of fabrication can include forming a core-shell quantumstructure of the one or more clusters of nanowires 310. The core-shellquantum structure can include one or more core quantum structures and ashell quantum structure, as described above with reference to FIG. 1 inmore detail. At 440, a first quantum active region 120 can be formed oneach nanowire in the one or more clusters. In one implementation, IndiumGallium Nitride (InGaN) can be formed by selective area epitaxy on theSilicone doped GaN of the lower portions of the one or more clusters ofnanowires to form the first quantum active region 120 with a height ofapproximately 5 nm. The InGaN can be deposited using plasma assistedMBE, wherein the growth conditions can include a substrate temperatureof approximately 600° C., a Ga BEP of approximately 9×10⁻⁹ Torr and InBEP of approximately 7.5×10⁻⁸.

At 450, a first quantum barrier region 130 can be deposited. In oneimplementation, Aluminum Gallium Nitride (AlGaN) can be formed byselective area epitaxy on the InGaN for form the first quantum barrierregion 130 with a height of approximately 5 nm. For example, the AlGaNcan be deposited using plasma assisted MBE, wherein the growthconditions can include a substrate temperature of approximately 600° C.,a Ga BEP of approximately 9×10⁻⁹ Torr, and Al BEP of approximately4.5×10⁻⁹. The incorporation of AlGaN in the quantum barrier region 130leads to the formation of an AlGaN or Aluminum-rich GaN shellsurrounding the one or more InGaN quantum active regions due to thesmaller Al adatom migration length compared to Ga and In adatoms.

An AlGaN compound semiconductor can be used for the quantum barrierregion 130 to achieve a nanowire having ultraviolet wavelengths ofemission. In another implementation, the quantum barrier region 130 caninclude Indium Gallium Arsenide (InGaAs) to achieve a nanowire havinginfrared wavelengths of emission. In yet another implementation, thequantum barrier region 130 can include Indium Arsenide (InAs) to achievea nanowire having mid-infrared wavelengths of emission.

The processes at 440 and 450 can be performed one or more times to formthe second portion of each nanowire in the one or more clusters. Forexample, the processes at 440 and 450 can be iteratively performed tentimes to form a second portion of the nanowires including ten quantumcore structures and a quantum shell structure disposed about theperiphery of the ten quantum core structures.

At 460, an upper portion of the nanowires 150 including a group III-Vcompound semiconductor with a second type of doping can be formed. Inone implementation, the group III-V compound semiconductor with thefirst type of doping can be p-dope Gallium Nitride (GaN). The groupIII-V compound semiconductor with the second type of doping can bedeposited by selective area epitaxy. For example, the upper portions ofthe nanowires 150 in the one or more clusters can be formed by selectivearea epitaxy of GaN with Magnesium (Mg) doping (e.g., p-doping) on topof a quantum barrier region and surrounding quantum shell structure 140using plasma assisted Molecular Beam Epitaxy (MBE) to form the upperportion of the nanowire 150 with height of approximately 30 to 80 nm.The growth conditions for the Mg-doped GaN can include a Ga BEP ofapproximately 3.5×10⁻⁷ Torr, a Mg BEP of approximately 2×10⁻⁹ and asubstrate temperature of approximately 750° C.

The incorporation of AlGaN in the one or more quantum barrier regions130 of the core-shell quantum structure 120-140, instead of GaN barriersas used in the conventional art, advantageously leads to the formationof the AlGaN quantum shell structure 140 surrounding the quantum corestructure 120, 130. This particular core-shell quantum structure 120-140formation process is due to the smaller Al adatom migration lengthcompared to Ga and In adatoms. The resulting core-shell quantumstructure 120-140 can advantageously suppress non-radiative surfacerecombination resulting an enhanced luminescence intensity andluminescence efficiency of the nanowires 310.

At 470, an optional optically transmissive insulator layer 345 can bedeposited on the substrate about the one or more clusters of nanowires.In one implementation, the insulator layer can be an opticallytransmissive polyimide layer conformally deposited on the substrate, andabout and on top of the one or more cluster of nanowires. The insulativelayer can be planarized, wherein tops of the one or more clusters ofnanowires are exposed and the optically transmissive insulative layer isdisposed between the one or more clusters of nanowires.

At 480, an optional first set of one or more layers of a first contact330-340 can be deposited on the planarized surface of the opticallytransmissive insulator layer 345 and the exposed tops of the one or moreclusters of nanowires 310. The first set of one or more layers of thefirst contact can be electrically coupled to the one or more clusters ofnanowires. In one implementation, a first layer of Nickle, Gold and/oralloys thereof can be deposited on the optically transmissive insulatorlayer and the exposed tops of the one or more clusters of nanowires. Thefirst layer of Nickle (Ni), Gold (Au) and/or NiAu alloys thereof can bedeposited as a very thin film that is configured to be substantiallyoptically transmissive. Alternatively, a masking and selective etchingprocess can be used to form one or more windows through the first layerof Nickle, Gold and/or alloys thereof. An Indium Tin Oxide (ITO) layercan be deposited on the first layer of Nickle (Ni), Gold (Au) and/orNiAu alloys thereof. The ITO layer can be configured to be opticallytransmissive. A second layer can be deposited on the ITO layer. Amasking and selective etching process can be used to form one or morewindows through the second layer of Nickle (Ni), Gold (Au) and/or NiAualloys thereof.

At 490, an optional second contact 350 can be deposited on the substrate320 opposite the one or more clusters of nanowires 310, the opticallytransmissive insulator layer 345 and first contact 330-340. In oneimplementation, a layer of Titanium (Ti), Gold (Au) and/or TiAu alloysthereof can be deposited on the substrate to form the second contact.

Referring now to FIGS. 6A-6D, exemplary nano-patterns, in accordancewith aspects of the present technology, as shown. The nano-pattern canrepresent the opening of a corresponding nano-pattern layer or thecross-section shape of nanowires formed therein. The nano-pattern caninclude one or more clusters of hexagonal, square, rectangular, rhombic,polygonal, circular, elliptical or similar cross-sectional shapedopenings/nanowires or combinations thereof, characterized by apredetermined spacing 610. These shapes are only a few examples of themany possible shapes that could be used in aspects of the presenttechnology.

Referring now to FIGS. 7, 8 and 9 , exemplary Scanning ElectronMicroscope (SEM) images of InGaN/AlGaN hexagonal nanowire structureswhich include dot-in nanowire, dot-in-nano-triangle, anddot-in-nano-rectangle arrays, are shown. The nanowire structures exhibitstraight sidewalls and uniform size distribution. The photonic moleculescan be arranged in various lattice structures, including rhombic 710,triangular 720 or hexagonal 730 lattices, with different orientations.The relative positioning of the nanowire structures with various shapescan form geometric shapes that can be for example of triangular shape740 or hexagonal shape 750 as depicted in FIG. 7 .

Take the nanowire array structure depicted in FIG. 8 , as an example. Inthis example, the nanowire structures 810 are hexagonal shaped and arearranged in a triangular lattice with a lattice constant 820 of 250 nmshown in the inset of the image. The nanowire structures have lateralsizes of 215 nm and length, also referred to as height, of 560 nm. Theair gap between neighboring nanowires is 35 nm. These nanowirestructures 810 as depicted in FIG. 8 can form a large array of nanowirestructures which could have a uniformity over a large area.

The uniformity of numerous InGaN nanowire structures across a large areais depicted in the Scanning Electron Microscope (SEM) image of FIG. 9 .In the image of FIG. 9 individual nanowire structures 910 are visible inthe form of tiny dots that form an array over the relatively large areaof 25 μm×25 μm. The size of this area could be much larger though, butvisible in the image is only a portion that is 25 μm×25 μm in size.

Referring now to FIG. 10 , a plot of an exemplary photoluminescenceemission spectrum of InGaN/AlGaN quantum nanowire structures measured atroom temperature as compared to a photoluminescence emission spectrum ofa conventional InGaN/AlGaN nanowire structures without controlledspacing, is shown. A plot of the photoluminescence emission spectrum ofInGaN/AlGaN quantum nanowire structures 1010 and a plot of thephotoluminescence emission spectrum of a conventional InGaN/AlGaNnanowire structures without controlled spacing 1020 is illustrated.Strong photoluminescence emission was observed at 505 nm wavelength witha relatively narrow spectral linewidth of approximately 12 nm for thephotonic crystals illustrated in FIG. 8 . The photoluminescence emissionis highly uniform across a large nanowire array structures. Forcomparison, conventional InGaN nanowire array structures or epilayersexhibit 1020 broad spectral linewidths of approximately 35-50 nm, at 507nm wavelength, which is limited by the large inhomogeneous broadeningassociated with Indium compositional variation and the presence ofdefects and strain field.

As illustrated in FIG. 10 , the photoluminescence intensity of theInGaN/AlGaN quantum nanowire structures 1010 is enhanced by nearly afactor of eight compared to InGaN/GaN nanostructures without theformation of an AlGaN shell 1020. Photoluminescence andcathodoluminescence material characterization techniques were used toassess the material quality of the fabricated nanowire array structures.In these experiments a 405 nm wavelength laser was used as theexcitation source for the photoluminescence measurement of theInGaN/AlGaN nanowire heterostructures. A visible neutral density filterwas used to adjust the laser excitation powers in range of 29 W/cm² to17.5 kW/cm². The emitted light was spectrally resolved by ahigh-resolution spectrometer, and was detected by a high sensitivity andlow noise liquid nitrogen cooled Charge Coupled Device (CCD) in thevisible range. Temperature dependent photoluminescence measurements werecarried out using a helium closed-loop cryostat. cathodoluminescencemeasurement was performed using a Zeiss Supra 55 VP field emission gunScanning Electron Microscope (SEM) equipped with a cryogenic stagecoupled to a Gatan MonoCL 2 setup. A gold thin film layer was depositedon the substrate in order to suppress charging effect induced by theelectron beam. The accelerating voltage used in the cathodoluminescencecharacterization was 10 KeV. The emission was collected by a parabolicmirror and detected using a dry-ice cooled photomultiplier tube.

Referring now to FIG. 11 , an exemplary plot of light intensity versusexcitation power of InGaN/AlGaN quantum nanowire structures as comparedto a conventional InGaN/AlGaN nanowire structures without controlledspacing, is shown. The integrated luminescence intensity (area under theplot) is nearly three times higher in the InGaN/AlGaN quantum nanowirestructures 1110 as compared to InGaN/AlGaN nanowire structures withoutcontrolled spacing grown under similar conditions 11120. The uniquedependence of the luminescence emission on the nanowire spacing andheight, as well as the impact of optical confinement of photoniccrystals on the temperature and power-dependent emission characteristicsof InGaN is described further below.

Referring now to FIG. 12 , a diagram of simulated photonic crystals, inaccordance with aspects of the present technology, is shown. Thephotonic crystals can be characterized by the parameters “M”, “K”, and“r” that were discussed earlier and are depicted in FIG. 5 with thenumerical indicators 530, 540, and 550 respectively are depicted here inFIG. 12 on the horizontal axis of the diagram.

The refractive index of InGaN nanowires is 2.37. The normalizedfrequency of the band-edge mode is approximately 0.49, which correspondsto a wavelength 1=505 nm for a lattice constant a=250 nm. By adjustingthe flat bands of leaky modes, (e.g., frequencies around 0.49) to matchthe emission wavelengths of the active region, the luminescenceefficiency can be significantly enhanced, due to the Purcell effect. Thegroup velocity can be determined by the slope of the dispersion curve inthe photonic band structure. At the band edge, a low group velocity canbe achieved, (i.e. dw/dk approaching 0) for frequencies around 0.49 nearthe F point, thereby leading to the formation of a stable and largecavity mode. The low group velocity and the resulting long interactiontime between radiation field and active material can lead to aconsiderably enhanced spontaneous emission rate. Moreover, due to Braggscattering, the light extraction efficiency can also be enhanced.

Referring now to FIG. 13 , an exemplary electric field profile, inaccordance with aspects of the present technology, is shown. Theelectric field profile 1310 of the band edge mode calculated by athree-dimensional finite-difference time-domain method for a band edgemode (λ=505 nm) for an areal size of 5 μm×5 μm over a range extendingfrom 1320 to 1330 as depicted by the color code bard 1340, isillustrated.

Referring now to FIGS. 14A-14C, exemplary cathodoluminescences forcrystals of different areal sizes, in accordance with aspects of thepresent technology, are shown. The formation of stable and scalableoptical modes in the bottom-up photonic crystals in accordance withaspects of the present technology is revealed by the cathodoluminescencestudies. In FIG. 14A, the cathodoluminescence 1410 was taken at awavelength of approximate 505 nm at room temperature. The areal sizebeing excited by the e-beam was 5 μm×5 μm. As illustrated, the band edgemode spreads across the entire crystal structure of hexagonally shapednanowire structures 1420. This is in agreement with the calculationshown in FIG. 13 . Strong light confinement occurs near the centerregion of nanowire arrays by the scattering of the band edge mode.Moreover, it is interesting to observe that strong photon confinementcan also be achieved for crystals with areal size as small as 2 μm×2 μmas depicted 1430 in FIG. 14B, and even as small as 1 μm×1 μm as depicted1440 in FIG. 14C. The results depicted in FIGS. 14A-14C confirm thescalability of the band edge modes.

Detailed cathodoluminescence measurements were also performed for InGaNphotonic crystals with different design parameters and at differentemission wavelengths. These results are depicted in FIGS. 15 and 16further below. These studies provided unambiguous evidence for theformation of strongly confined, highly uniform, and scalable band edgemodes of InGaN photonic crystals, thereby offering a viable approach forrealizing both small and large scale efficient light emitters.

FIG. 15 depicts the spectrally resolved cathodoluminescence mappingimages collected at various wavelengths of 370 nm, 450 nm, 505 nm and520 nm, respectively. These results are evidence of the presence of bandedge mode and strong optical confinement effect only at an emissionwavelength of 505 nm.

FIG. 16 depicts a cathodoluminescence mapping image at the wavelength of505 nm for InGaN nanowire arrays with a relatively large spacingcompared to the optimum design depicted in FIG. 15 , showing the absenceof the band edge mode. Due to the weaker emission for the image shown inFIG. 16 , the measurement was performed with a relatively longintegration time to clearly show the light distribution.

Further extensive studies were performed on InGaN nanowire structureswith different design parameters. Referring now to FIG. 17 , exemplaryplots associate with the variations of the luminescence intensity andspectral linewidth, in accordance with aspects of the presenttechnology, is shown. The variations of the luminescence intensity andspectral linewidth with varying nanowire spacing while keeping thelattice constant parameter a constant are illustrated. The plots 1710and 1720 depict the variations of the integrated luminescence intensity1730 and Full Width Half Maximum (FWHM) 1740 of InGaN nanowirestructures versus nanowire spacing 1750.

Crystal growth epitaxy conditions were optimized to have similarspontaneous emission from the quantum dot active regions when thenanowire spacing is varied. In FIG. 18 , it is seen that the emissioncharacteristics, in terms of both the spectral linewidth and integratedintensity, depend critically on the nanowire spacing. The highestluminescence intensity and narrowest spectral linewidth occurs for ananowire spacing of 35 nm. A decrease, or increase in nanowire spacinglead to a reduction in the luminescence intensity, accompanied by asignificant increase in the spectral linewidth, which suggests areduced, or minimal level of coupling between the quantum dotspontaneous emission and the band edge mode. Since the light extractionefficiency of leaky modes does not change significantly for such smallvariations of nanowire spacing, the measured variations of luminescenceemission may be primarily attributed to the change of the Purcelleffect. Based on the measured internal quantum efficiency ofapproximately 2 to 30% at room-temperature for the InGaN photoniccrystals, and assuming a constant light extraction efficiency, themagnitude of Purcell enhancement factor (Fp) is estimated to be in therange of 3 for the spatially extended band edge mode, which iscomparable to that for the very small mode in a nanocavity. Therelatively large Purcell factor is partly related to the large modedegeneracy factor g depicted in Equation 2 associated with the largemodal volume. The extreme sensitivity of the Purcell effect on thenanowire spacing (radius) was not seen in conventional slab photoniccrystals, which is partly related to the quasi three-dimensional natureof InGaN nanowire photonic crystals, due to the presence of planar GaNsubstrate as well as the finite length of InGaN nanowires. Thisobservation is further supported by the critical dependence of theemission characteristics of InGaN nanowire photonic crystals on theheight of nanowires as illustrated in. FIGS. 1 and 18 .

Due to the presence of quantum-confined Stark effect, conventional InGaNlight emitters generally exhibit significant blueshift with increasingpumping power. Moreover, the emission characteristics also varyconsiderably with temperature, due to the Varshni's effect. In contrast,we have measured remarkably stable emission characteristics for InGaNnanowire photonic crystals. Depicted in FIG. 19 are the normalizedphotoluminescence emission spectra of InGaN photonic crystals measuredat excitation power from 29 W/cm² to 17.5 KW/cm² at room-temperature.From the ten plots 1910A to 1910J, it is seen that the emission spectraremains nearly identical. In the diagram the horizontal axis 1920indicates the wavelength in units of nm and the vertical axis 1930indicates the normalized photoluminescence intensity in arbitrary units(a.u.).

Referring now to FIG. 20 , exemplary plots of the peak emissionwavelength and spectral linewidth versus pumping power, in accordancewith aspects of the present technology, are shown. In the diagram, thevertical axis 2010 indicates FWHM in units of nm, the other verticalaxis 2020 indicates the wavelength of emission in units of nm, and thehorizontal axis 2030 indicates the excitation power density in units ofKW/cm². As illustrated, the peak emission wavelengths 2040, atapproximately 505 nm, and the spectral linewidths 2050, FWHM atapproximately 12 nm, are virtually invariant as a function of pumpingpower.

Referring now to FIG. 21 , exemplary plots of luminescence emissionspectra of InGaN nanowire structures, in accordance with aspects of thepresent technology, are shown. In the diagram, the horizontal axis 2110indicated the wavelength of emission in units of nm and the verticalaxis 2120 indicates the normalized photoluminescence intensity inarbitrary units (a.u.). As depicted, luminescence emission spectra weremeasured in the temperature range of 5 to 300 Kelvin (° K) in the tenplots 2130A-2130J. The results were measured under 8.7 KW/cm² continuouswave pumping condition.

Referring now to FIG. 22 , exemplary plots associated with thevariations of the emission wavelength peak with temperature and thevariations of spectral linewidth with temperature, in accordance withaspects of the present technology, are shown. In the diagram, thevertical axis 2210 indicates the wavelength of emission in units of nm,the other vertical axis 2220 indicated the FWHM parameter in units ofnm, and the horizontal axis 2230 indicates the temperature in units of °K. As illustrate, both the emission wavelengths 2240, at approximately505 nm, and spectral linewidths 2250, at approximately 12 nm, remainednearly constant in the temperature range of 5 to 300° K. The remarkablystable emission characteristics of InGaN nanowire structures aredrastically different from the commonly measured S-shape dependence ontemperature for conventional InGaN quantum wells, induced by chargecarrier redistribution in the localized states and bandgap reductionwith increasing temperature. Such extraordinary emission stability stemsdirectly from the efficient coupling of InGaN quantum dot emission tothe robust band edge modes of InGaN photonic crystals, which isvirtually independent of device operating conditions and largelydetermines the emission characteristics.

Referring now to FIG. 23 , an array of nanowire structures and anassociated photoluminescence emission pattern, in accordance withaspects of the present technology, is shown. For the array of nanowirestructures 2310, 2320, the photoluminescence emission pattern 2330 andthe spectral curve 2340 of the photoluminescence emission, at awavelength of approximately 505 nm 2350 as indicated by the FWHM valueof approximately 12 nm 2360 are depicted.

Referring again to FIG. 9 , the image of a 450 tilted-view SEM image ofthe InGaN nanowire structure, in accordance with aspects of the presentinvention, is shown. As depicted, individual nanowire structures 910 arevisible in the form of tiny dots that from an array over a relativelylarge area. The size of the area covered by the nanowire array could bemuch larger than the 25 μm×25 μm that is visible in the image of thesample The image is evidence of extremely high uniformity across a largearea.

FIGS. 24 and 25 illustrate the measurement results associated with theemission stability of InGaN nanowire structures across a large area. Theimage in FIG. 24 is part of an experiment that was conducted in order toinvestigate the emission characteristics, including the uniformity andyield of InGaN nanowire structures fabricated in a large area. Asillustrated in FIG. 24 , six different points 2410 were measured in anarea the size of 100 μm×100 μm. In this photoluminescencecharacterization experiment a 405 nm wavelength laser was used as theexcitation source at room temperature. As illustrated in FIG. 25 , theemission wavelengths, which are depicted by plot 2510, remain nearlyinvariant, at approximately 505 nm for various regions 2410 that aredepicted in FIG. 24 of the nanowire structure. Also illustrated in FIG.25 is the plot 2520 of FWHM values, that depict a narrow spectrallinewidth of approximately 12 nm, is also nearly invariant for thevarious measurement points. In the plots of FIG. 25 , the vertical axis2530 indicates the wavelength value in units of nm, the other verticalaxis 2540 indicates the FWHM values, and the horizontal axis 2550indicates the 6 various measurement points 2410 that are depicted inFIG. 24 . The extremely high yield and uniformity is attributed to thewell-controlled nanowire size and position of the unique selective areaepitaxy.

Referring again to FIG. 15 and FIG. 16 , the images associated withcathodoluminescence mapping measurement results spectrally resolved atdifferent emission wavelengths and with different design parameters areillustrated. To further confirm the formation of stable band edge modesin InGaN photonic crystals, more detailed spectrally resolvedcathodoluminescence mapping measurements were performed at differentwavelengths.

FIG. 15 depicts the spectrally resolved cathodoluminescence mappingimages 1510, 1520, 1530 and 1540 collected at various wavelengths of 370nm, 450 nm, 505 nm and 520 nm, respectively, demonstrating the presenceof band edge mode and strong optical confinement effect only at anemission wavelength of 505 nm. The cathodoluminescence image 1510 at 370nm exhibits highly uniform contrast in the entire region. It was alsonoticed the spacing between nanowires shows brighter emission, which isdue to the light emission from the underlying GaN template.

FIG. 16 depicts a cathodoluminescence mapping image at the wavelength of505 nm for InGaN nanowire arrays with a relatively large spacingcompared to the optimum design depicted in FIG. 15 , showing the absenceof the band edge mode. Due to the weaker emission for the image shown inFIG. 15 , the measurement was performed with a relatively longintegration time to clearly show the light distribution. Depicted inimage the of FIG. 15 are the hexagonal cross sections of the nanowirestructures with a lattice constant parameter “a” which is 360 nm and thenanowire lateral lattice size “d”, which is 215 nm.

No emission was observed at 450 nm wavelength since there is no lightemission from the nanowires in this wavelength. At 505 nm, strongoptical confinement effect at the center region of nanowire arrays wasclearly observed. Significantly weaker emission was also measured at 520nm. These studies provide unambiguous evidence for the directmeasurement of the band edge mode in defect-free nanowire structures.Also performed were cathodoluminescence wavelength mapping measurementsof InGaN nanowire arrays with a relatively larger spacing compared tothe optimum design. The image taken at a wavelength of 505 nm isdepicted in FIG. 14A, and no optical confinement effect was observed.

Referring now to FIG. 26 , plots of the photoluminescence emissionspectra of exemplary nanowire devices, in accordance with aspects of thepresent technology, is shown. Five InGaN/AlGaN nanowire structures wereinvestigated, which had substantially identical designs except for theheight of the n-GaN lower portion which was varied from approximately380 to 460 nm 2610A-2610E. The nanowire structure included a n-GaNsegment 110, an quantum structure 120-140 that included ten verticallyaligned InGaN/AlGaN quantum dots 120, 130, and a 30 nm p-GaN layer 150with a hexagonally pyramid-like top. The quantum dots structure includedmultiple layers of InGaN 120 and AlGaN 130, that were surrounded with anAl-rich GaN shell 140 substantially similar to the nanowire illustratedin FIG. 1 .

For the plots in FIG. 26 , the photoluminescence emission spectra of theInGaN nanowires were measured at room temperature with a 405 nmwavelength laser as the excitation source. Strong emission was observedat a wavelength of approximately 510 nm with a relatively narrowspectral linewidth of approximately 6 nm for nanowire arrays withheights varying from approximately 550 to 590 nm, as illustrated in FIG.26 . In the plot the horizontal axis 2610 indicates the wavelength ofemission in units of nm and the vertical axis 2610 indicates thenormalized PL intensity in arbitrary units (a.u.). However, the lightintensity showed a significant decrease when the nanowire height wasreduced below 550 nm, accompanied by a significantly broadenedlinewidth. These studies show that the band edge mode and the Purcelleffect depends critically on the nanowire height, in addition to thenanowire diameter and spacing.

In according with aspects, the present techniques successfullydemonstrate the bottom-up synthesis of InGaN photonic molecules withprecisely controlled size, spacing, and morphology, which can serve asthe fundamental building blocks of a new generation of photonic crystaldevices and systems. By coupling the light emission into the band edgemode of InGaN nanowire structures, significantly enhanced emissionefficiency and reduced spectral broadening was measured. Moreover, theluminescence emission exhibits remarkable stability. There are virtuallyno variations in the emission characteristics, in terms of both theemission wavelength peak and also the spectral linewidth in thetemperature range of 5 to 300° K and for pumping power variations from29 to 17.5 kW/cm². To our knowledge, this is the first demonstration ofthe absence of quantum-confined Stark effect and Varshni's effect inInGaN light emitters. These unique characteristics, together with thescalable band edge optical mode, high light extraction efficiency,on-demand beam characteristics, and full-color emission, renderbottom-up GaN nanowire photonic crystals well suited for ultrahighefficiency, large area LED and laser devices as well as integratednanophotonic circuits in the ultraviolet and visible spectral range.

The foregoing descriptions of specific embodiments of the presenttechnology have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the present technology and its practicalapplication, to thereby enable others skilled in the art to best utilizethe present technology and various embodiments with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto and their equivalents.

What is claimed is:
 1. A method of fabricating a nanowire comprising;forming by Selective Area Growth (SAG) a first semiconductor nanowireregion with a first type of doping; forming by SAG a quantum structureon the first semiconductor nanowire region, the quantum structureincluding one or more quantum core structures and a quantum shellstructure disposed about a periphery of the one or more quantum corestructures; and forming by SAG a second semiconductor nanowire regionwith a second type of doping on the quantum structure.
 2. The method offabricating the nanowire of claim 1, wherein forming by SAG a quantumstructure comprises: forming by SAG a quantum active region; and formingby SAG a quantum barrier region on the quantum active region.
 3. Themethod of fabricating the nanowire of claim 1, wherein: forming by SAGthe quantum active region includes epitaxially depositing Indium GalliumNitride (InGaN); and forming by SAG the quantum barrier region includesepitaxially depositing Aluminum Gallium Nitride (AlGaN), wherein thequantum core structure is formed from layers of the Indium GalliumNitride (InGaN) and the Aluminum Gallium Nitride (AlGaN) and the quantumshell structure is formed from the Aluminum Gallium Nitride (AlGaN). 4.The method of fabricating the nanowire of claim 1, wherein: forming bySAG the first semiconductor nanowire region with the first type ofdoping includes epitaxially depositing n-type doped Gallium Nitride(GaN); and forming by SAG the second semiconductor nanowire region withthe second type of doping includes epitaxially depositing p-type dopedGallium Nitride (GaN).
 5. A method of fabricating a device including oneor more clusters of nanowires comprising: forming a nano-pattern layerincluding one or more cluster of openings; forming a first semiconductorregion with a first type of doping disposed in the one or more clusterof openings in the nano-pattern layer; forming a quantum structure onthe first semiconductor region, the quantum structure including one ormore quantum core structures and a quantum shell structure disposedabout a the one or more quantum core structures; and forming a secondsemiconductor region with a second type of doping disposed on thequantum structure.
 6. The method according to claim 5, wherein formingthe nano-pattern layer comprises: depositing a Titanium (Ti) layer on asubstrate; forming a nano-pattern mask on the Ti layer, wherein thenano-pattern mask includes one or more clusters of openings; andselectively etching the Ti layer exposed by the one or more clusters ofopening in the nano-pattern mask.
 7. The method according to claim 6,wherein forming the first semiconductor region with the first type ofdoping comprises epitaxially depositing n-type doped Gallium Nitride(GaN).
 8. The method according to claim 7, wherein forming the quantumstructure comprises: epitaxially depositing one or more layers of IndiumGallium Nitride (InGaN); and epitaxially depositing one or more layer ofAluminum Gallium Nitride (AlGaN) interleaved between the one or morelayers of Indium Gallium Nitride (InGaN) and about a periphery of theone or more layers of Indium Gallium Nitride (InGaN).
 9. The methodaccording to claim 8, forming the second semiconductor region with thesecond type of doping comprises epitaxially depositing p-type dopedGallium Nitride (GaN).
 10. The method according to claim 9, furthercomprising forming a nucleation layer between a substrate and thenano-pattern layer.
 11. The method according to claim 9, furthercomprising: depositing an optically transmissive insulator on asubstrate between the one or more clusters of nanowires: forming one ormore first contacts on the optically transmissive insulator layer andelectrically coupled to the one or more clusters of nanowires; andforming a second contact on the substrate opposite the one or moreclusters of nanowires, wherein the second contact is electricallycoupled to the one or more clusters of nanowires through the substrate.12. The method according to claim 5, wherein the openings in thenano-pattern layer have a hexagonal, square, rectangular, circular,elliptical or polygonal cross-sectional shape.
 13. The method accordingto claim 5, wherein the one or more quantum core structures include aplurality of quantum disks, quantum arch-shaped forms, quantum wells,quantum dots within quantum wells or combinations thereof.